The present invention relates to a piston designed for use in a compression ignition (diesel) internal combustion engine. More particularly, the present invention relates to a combustion chamber defined in the crown of a piston.
Many attempts have been made to produce an ideal flow pattern for the charge of air and fuel within the combustion chamber of an internal combustion engine. Considerations that must be taken into effect include, but are not limited to, providing for adequate power generation minimizing the NOx entrained in the engine exhaust and minimizing the amount of soot particulate also entrained in the engine exhaust.
It is known that changes in any one of a variety of engine design/operating variables, such as engine compression, combustion chamber shape, fuel injection spray pattern, and other variables can have an effect on both emissions and power generated.
The amount of soot that is expelled with the engine""s exhaust is unsightly and generates public pressure to clean up diesel engines. Further, the amount of soot that is entrained in the engine""s lubrication oil can have a deleterious effect on engine reliability. Soot is very abrasive and can cause high engine wear.
There is additionally a great deal of pressure to reduce the NOx emissions from the engine. Ever increasing regulatory demands mandate reduced levels of NOx. Typically, a combustion chamber design that is effective at reducing NOx levels has been found to increase the levels of soot and vice-versa. Additionally, doing either of the aforementioned typically reduces engine torque and power outputs.
There are numerous examples of combustion chambers formed in the crown of piston. Notwithstanding all these prior art designs, there remains a need for reduction both in NOx and entrained soot while at the same time maintaining or enhancing engine torque and power outputs.
The piston of the present invention substantially meets the aforementioned needs of the industry. The combustion chamber of the present invention defined in the crown of the piston has been shown by substantiated simulation to both reduce soot entrainment and NOx emissions while at the same time maintaining engine power output. The corresponding diesel engine experimental results support the simulation. The piston has been shown to function effectively with cylinder heads having two or more valves. A further advantage of the piston of the present invention is that by being symmetrical with respect to a piston central axis, the combustion chamber is relatively easily formed in the crown of the piston. The piston and combustion chamber of the present invention are preferably used in heavy-duty and medium-duty diesel engines.
The present invention is a combustion chamber assembly for use in a diesel engine includes a combustion chamber defined in a crown of a piston, the combustion chamber having a center portion, the center portion being defined at least in part by a portion of a convex sphere, the sphere having a radius and an origin, the origin of the radius lying on a piston central axis and the combustion chamber further having an outwardly radially disposed bottom margin, the bottom margin being defined in part by a portion of an annulus, the annulus having a radius and an origin. The combustion chamber further has a plurality of curved surfaces having smooth transitions between adjacent smooth surfaces, the smooth surfaces including the spherical center portion and the annular bottom margin. The present invention is further a piston incorporating the aforementioned combustion chamber and a method of forming the combustion chamber.